The contamination of subsurface soils and water with arsenic is a well-documented problem, due to the toxic and carcinogenic effects of such compound. Naturally occurring arsenic or arsenic which is present through human activities can contaminate groundwater as the water passes through contaminated soil. Such contaminant may then be transported into drinking water sources, lakes, and rivers from such groundwater. The arsenic present in soil and/or groundwater is generally present as arsenite (As(III)) or arsenate (As(V)) species. As is noted by Magalhaes, Arsenic. An environmental problem limited by solubility. Pure Appl. Chem Vol. 74, No. 10, pp. 1843-1850 (2002), arsenite species are more toxic than arsenates, with metal arsenites being much more soluble in water than their corresponding metal arsenates.
The art has attempted to address remediation of soil and groundwater contaminated with arsenic through a variety of methods. Among the methods which have been employed is the precipitation of metal arsenates, particularly of calcium, magnesium and iron (III) arsenates. However, Magalhaes, cited above, concludes that such methods are “unlikely to produce aqueous solutions with arsenic concentrations below the guideline values proposed for arsenic dissolved in potable water and treated sewage effluents” (Abstract).
Clifford et al, Oxidizing Arsenic III to Arsenic V for Better Removal, Water and Wastes Digest, Aug. 13, 2011, discloses that processes to remove arsenic from water which rely on anion removal (including anion exchange and activated alumina adsorption) are only effective when the As(III) present is first oxidized to As(V). However, this publication stresses that such oxidation treatment should occur in the absence of sulfates, stating that “high sulfate concentration negatively affects the ion exchange process”.
Accordingly, it is entirely unexpected that a process which relies on sulfate radicals to oxidize As(III) to As(V) which is then precipitated to form stable, water insoluble materials, would be effective to reduce the content of soluble arsenic present in soil and/or water.